The results of the LUX experiment are out - and they are negative: no dark matter signal has been spotted by the extra sensitive detector. This is a normal day for you and me, but a gloomy day for those that counted on the neutralino to be the first supersymmetric particle to show up and redeem decades of claims.

Flippant comments aside, the experiment is a technological marvel. Located one mile underground at Sanford Laboratory, it is a water-shielded tank containing 250 kg of liquid xenon as active material. The deep underground location, combined with the exceptional purity of the xenon and the high efficiency of electron recoil detection, guarantees a high sensivity to the weak signal of neutralinos, or whatever other neutral, weakly-interacting particle dark matter is made of.

The search was described, along with a number of technical details, nice pictures, and complicated graphs, in a talk given today by the spokespersons of the experiment, Rick Gaitskell and  Dan McKinsey. You can find the slides at this link.

They also produced a draft of a Physical Review Letters article, but the article was taken off the web very quickly after it appeared. The abstract however reads as follows:

The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. We report results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6 × 10−46 cm2 at a WIMP mass of 33 GeV/c2. We find that the LUX data are in strong disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments."

So, LUX reachs down to extremely small cross sections, and still there is no hint of neutralinos permeating the universe and hitting the xenon atoms, not even for ready money. I do not rejoice - I would be as happy as you both if we found Supersymmetry in WIMP-matter interactions or in LHC collision data, so the result is not welcome. However, it confirms my beliefs that Supersymmetry is not the explanation of the composition of matter in the universe any more than it is a solution to the hierarchy problem.






 


 The detector was fully commissioned in April this year, and the results reported are based on three months of data taking; a year-long run will follow in 2014.